#include<stdio.h>
#include<math.h>

long long int P,i,aux,aprox,count;
long long int coef(long long int x)
 {long int nr=0;

  while(x%5==0)
   {
    x/=5;
    nr++;
   }
  return nr;
 }


int main()
{
FILE*in=fopen("fact.in","r");
FILE*out=fopen("fact.out","w");
fscanf(in,"%lld",&P);
aprox=5*P;
i=2;
count=P;
while(pow(5,i)<=aprox)
 {
  count+=aprox/pow(5,i);
  i++;
 }
while(count!=P)
 {
  aux=aprox;
  aprox-=5;
  count-=coef(aux);
 }

fprintf(out,"%lld",aprox);
fcloseall();
return 0;
}